1. Field of the Invention
The present invention is directed to a drug delivery system and, in particular, to a closed loop system and method for controlling muscle activity by infusion of drugs, e.g., antispasmodic drugs, via an intrathecal/intraspinal catheter.
2. Description of Related Art
Muscle disorders can have debilitating effects on an individual's daily life. It is desirable to administer drugs to reduce or control undesirable muscle activity. By way of example, spasticity is an abnormal involuntary muscle activity with increased muscle tone (rigidity) and sustained muscle contractions (spasm) caused by damage to the central nervous system resulting, for example, from a spinal cord or head injury. Often spasticity is but a symptom associated with a disorder such as multiple sclerosis, cerebral palsy, stroke, Parkinson's or Epilepsy.
There is a widespread degree of spasticity ranging from moderate to severe. Moderate spasticity may have little interference in the patient's normal life and typically is controlled by physical therapy and/or oral muscle relaxants. Patients that suffer from severe spasticity may be treated by way of intrathecal therapy administering the drug directly to the spinal subarachnoid space via an implantable pump. There are two main types of pumps that can be implanted for administration of drug via the intrathecal catheter. A fixed rate pump may be used to control the drug dosage, but this device does not permit dosage adjustment. Alternatively, a pump may be used that is capable of being programmed by a physician via an external battery powered computer to alter the drug dosage. This, however, is still disadvantageous in that it requires a physician or clinician to adjust or control the drug dosage. It would be desirable to adjust the drug dosage automatically without intervention by a physician or clinician.
Other types of undesirable muscle activity may likewise have a negative impact on one' daily activities and life. U.S. Pat. No. 6,263,237 discloses a method for the treatment of anxiety disorders by brain stimulation and drug infusion. Specifically, closed-loop feedback infusion of medicine and stimulation directly to the brain is disclosed in response to an electromyograph (EMG) sensor signal. The EMG sensor signal detects anxiety disorder related symptoms, e.g., excessive muscle tension or tremors. Since anxiety is controlled by the neural circuitry of the brain, the drug is delivered directly to the brain. This patented method closed-loop feedback infusion of antianxiety drugs directly to the brain based on the detection of muscle activity is disclosed exclusively for the treatment of anxiety disorders.
It is therefore desirable to subside, reduce, eliminate or control muscle activity by developing a closed loop feedback drug delivery system for the infusion of a drug directly to the spinal cord the dosage of which is automatically controlled based on detected muscle activity without intervention by a physician or clinician.